1. Field of the Invention
The present invention relates to a pivotable vertical strake located on the upper surface of the nose section of an aircraft forebody.
2. Description of Related Art
High performance aircraft must be capable of providing aerodynamic stability and control even at high angles of attack. More particularly, the aircraft must have the ability to roll robustly about the velocity vector of the plane. Lateral and directional control is typically accomplished through aft control surfaces such as wing ailerons and the tail rudder. At high angles of attack, the wash of the wing decreases the effectiveness of the rudder in controlling the aircraft. For this reason there has been increasing interest in utilizing forebody vortex control for aircraft flying at high angles of attack. Manipulating the forebody vortices can result in a side force on the forebody which creates a yawing moment on the aircraft.
Malcolm, G. N., "Forebody Vortex Control", Progress in Aerospace Sciences, Vol. 28, pp. 171-234, 1991 provides a general discussion on the various approaches to controlling forebody vortices including strakes located on the surface of the forebody and pneumatic systems with blowing jets or slots.
The use of fixed strakes on the forebody has been found to eliminate natural asymmetries in the flow and to prevent the aircraft from departing at high angles of attack. Fixed strakes typically have large surface areas that have been found to interfere with the imaging capability of the plane's radar, which is typically located in the forebody of the aircraft. Additionally, the strakes add stress to the structure of the radome. U.S. Pat. No. 5,207,397 issued to Ng et al, discloses a pair of strakes that are coupled to the nose section and can rotate about the longitudinal axis of the aircraft. The rotatable strakes were found to provide active vortex control about the forebody of the plane. It would be desirable to provide a more effective vortex control device than the systems deployed in the prior art.